This invention relates generally to dry low NO.sub.x gas turbine combustors and more particularly concerns an apparatus for reducing unsteady high frequency transverse oscillations in such combustors.
In power plant design, reducing emissions of harmful gases such as NO.sub.x into the atmosphere is of prime concern. Lean premixed combustion is one approach to lowering NO.sub.x emissions. In lean premixed combustion, fuel and air are premixed in a premixer section prior to combustion in the main combustion chamber. Due to the lean stoichiometry, lean premixed combustion achieves lower flame temperatures and thus produces lower NO.sub.x emissions. However, most advanced premixed combustor designs are susceptible to large unsteady pressure oscillations termed screech because of the turbulent nature of the combustion process and the large volumetric energy release within the closed cavities of the combustor. If not suppressed, screech will severely limit the operation of the device and in some cases can even cause physical disintegration of combustor hardware. Acoustic, energy-absorbing liners are conventionally used to suppress screech. However, these liners are costly and allow air leakage which may have an adverse impact on combustor performance and emission levels.
Accordingly, there is a need for a means to suppress the combustion-induced unsteady pressure oscillations in lean premixed gas turbine combustors without adversely affecting the emissions quality or the operation. There is an additional need for a means to suppress screech which requires only a minimal change in hardware.